fix: license should be a valid SPDX license expression
fix: license should be a valid SPDX license expression

when `npm install` on the repo or a fork, npm complains that license
field in package.json is not valid.

See https://docs.npmjs.com/files/package.json#license
for valid `license` expressions

Same applies for bower.json:
https://github.com/bower/spec/blob/master/json.md#license

Both must be a string containing a valid SPDX license identifier:
https://spdx.org/licenses/

goldfire/howler.js,goldfire/howler.js